Dispersing apparatus

ABSTRACT

In a dispersing apparatus comprising a container ( 10 ) for a dispersion material, a dissolve disc ( 22 ) drivable by a shaft ( 21 ) and a grinding device which contains a grinding medium and which has a perforated housing ( 34 ) through which dispersion material can pass by virtue of a flow generated by the dissolve disc ( 22 ), and an agitator tool which is drillable by a drive element and which is arranged in the housing ( 34 ) and is rotatable relative thereto, wherein the housing ( 34 ) surrounds the shaft ( 21 ), wherein the housing ( 34 ) is displaceable relative to the shaft ( 21 ) from a raised position into a lowered position and wherein the shaft ( 21 ) and the drive element can be coupled together by way of a coupling which has a first element ( 47 ) and a corresponding second element ( 53 ), which elements are in operative connection in the lowered position, in order to design same in such a way than a dispersing apparatus comprising a container ( 10 ) for a dispersion material, a dissolve disc ( 22 ) drivable by a shaft ( 21 ) and a grinding device which contains a grinding medium and which has a perforated housing ( 34 ) through which dispersion material can pass by virtue of a flow generated by the dissolve disc ( 22 ), and an agitator tool which is drivable by a drive element and which is arranged in the housing ( 34 ) and is rotatable relative thereto, wherein the housing ( 34 ) surrounds the shaft ( 21 ), wherein the housing ( 34 ) is displaceable relative to the shaft ( 21 ) from a raised position into a lowered position and wherein the shaft ( 21 ) and the drive element can be coupled together by way of a coupling which has a first element and a corresponding second element, which elements are in operative connection in the lowered position, in order to design same in such a way that it complies with coming anti-explosion regulations and is of a simple structure, it is proposed that the first element of the coupling is arranged at the lower end of the housing ( 34 ) and that the second element of the coupling is arranged in the region of a lower end of the shaft ( 21 ).

The invention concerns a dispersing apparatus comprising a receivingcontainer for a dispersion material, a flow-generating device drivableby a shaft and a grinding device which contains a grinding medium andwhich has a perforated housing through which the dispersion material canpass by virtue of a flow generated by the flow-generating device, and anagitator tool which is drivable by a drive element and which is arrangedin the housing and is rotatable relative thereto, wherein the housingencloses the shaft, wherein the housing is displaceable relative to theshaft from a raised position into a lowered position, and wherein theshaft and the drive element can be coupled together by way of a couplingwhich has a first element and a corresponding second element, whichelements come into operative relationship in the lowered position.

An apparatus of that kind provides for the distribution of finely andvery finely divided solid constituents in the liquid phase. In thedispersing process three sub-steps take place in mutually parallelrelationship:

1. wetting of the surface of the solid material to be incorporated byliquid constituents of the grinding material;

2. mechanical breakdown of agglomerates into smaller agglomerates andprimary particles, and

3. stabilization of primary particles, agglomerates and aggregates toprevent renewed consolidation (equal to flocculation).

To implement an economical dispersion process the dispersion materialhas to be pre-dispersed. Preferably it is pre-dispersed with a dissolverdisc as, particularly when dealing with agglomerates which are difficultto disperse and which in the further procedure still require the use ofthe grinding device, optimum pre-dispersion is indispensable foreconomic reasons. An inadequately pre-dispersed product requires notonly longer run times for the grinding device, but frequently thedesired levels of fineness are not achieved. Omissions or errors in thepre-dispersing operation generally cannot be compensated or can becompensated only at a disproportionately high level of complication andexpenditure by means of other systems. That is in particular becauseinadequately pre-dispersed products, with further use of the grindingdevice, cause the holes in the sieve basket to become clogged, wherebycirculation through the sieve basket becomes more difficult or is evencompletely prevented.

Frequently however the dissolver can only implement pre-dispersion, thatis to say the dispersion material can be dispersed only down to acertain degree of fineness. For further dispersion, which is referred toherein as fine dispersion, it is necessary to use an agitator ball millor similar grinding device.

For the purposes of avoiding the container change between thepre-dispersing and the fine dispersing operations, European patentspecification No 0 850 106 to the present applicants proposes that thegrinding device is in the form of a housing which encloses the shaft andwhich is also displaceable in respect of height, relative to the shaft.During the pre-dispersing operation the grinding device is arranged inthe raised position above the dispersion material; for the finedispersing operation, the grinding device is transferred into thelowered position and moved into the dispersion material so that it isdisposed just above the flow-generating device in the form of thedissolver disc. In that apparatus the drive element for the agitatortool is in the form of a hollow shaft which encloses the shaft and whichis displaced together with the grinding device in the movement inrelation to the shaft. An arcuate tooth coupling is operative betweenthe shaft and the hollow shaft, the coupling transmitting the torquefrom the shaft to the hollow shaft only in the lowered position of thegrinding device, and that hollow shaft in turn being connectednon-rotatably at its lower end to the agitator tool.

That known dispersing apparatus requires a not inconsiderable degree ofcomplication and expenditure to prevent the dispersion material frompenetrating into the intermediate space between the shaft and the hollowshaft; ultimately that can never be one hundred percent avoided.

Forces of the dispersion material in the pre-dispersing operationapplied to the shaft, when the grinding device is in the raisedposition, can give rise to unwanted deflection of the shaft throughseveral millimeters. The result of that deflection can be that the shaftcomes into contact with and damages a plain bearing arranged in thegrinding device for carrying the shaft. A gap must be provided betweenthe plain bearing and the shaft for satisfactory functionality. Evenwith the most accurate structure, the chain of tolerances which areadded together, particularly in the case of relatively large dispersingdevices, means that it is not possible to prevent the dispersionmaterial passing through that gap into the intermediate space betweenthe hollow shaft and the shaft. In the event of damage to the plainbearing due to the above-mentioned unwanted shaft deflection during thepre-dispersing operation, those problems are made even worse. Inaddition the known structure, using the hollow shaft, requires anextremely slender bearing flange which at its lower end is supported byway of a needle bearing on the pinion of the arcuate tooth coupling; inthe case of larger dispersing apparatuses that slender bearing flangedoes not afford the required stability.

New anti-explosion regulations such as for example ATEX 95 (EU Directive94/9/EC) for rooms which are at risk of explosion will finally soonprescribe compulsory sealing integrity in respect of the hollow spacebetween the hollow shaft and the shaft. The above-indicated problemsmean that further complication and expenditure is required for sealingoff that space.

Accordingly the object of the present invention is to at least partiallyavoid the above-specified disadvantages, to design the dispersingapparatus in such a way that it complies with coming anti-explosionregulations, and to simplify the structure of the dispersing apparatus.

According to the invention that object is attained in that the firstelement of the coupling is arranged at a lower end of the housing andthat the second element of the coupling is arranged in the region of alower end of the shaft.

In accordance with the invention therefore the coupling is no longeroperative above but below the grinding device. Instead, the firstcoupling element of the coupling is arranged in the lower end of thehousing. The corresponding second coupling element of the coupling isarranged at the lower end of the shaft, just above the flow-generatingdevice. The configuration according to the invention provides that thecoupling elements are only brought into engagement in the loweredposition of the grinding device and then transmit the torque of theshaft to the agitator tool. A hollow shaft which embraces the shaft isthus no longer required. Accordingly, there are also no expensive anddelicate sealing packing means for sealing off the hollow shaft withrespect to the shaft. That markedly simpler structure is substantiallyless expensive and makes it possible for the first time to afford adissolver and an agitator ball mill combined at the same price in oneunit. The structure according to the invention is in additionsubstantially lower in maintenance as no relatively large tolerancechains occur. Finally, because of the absence of the hollow shaft, thereis no longer any need for the bearing flange to be of a slenderconfiguration. Accordingly, with the design configuration according tothe invention, the bearing flange can have corresponding reinforcingstruts for affording even relatively large dispersing apparatuses thenecessary stability.

Preferably the second coupling element is arranged at the lower end ofthe shaft immediately above the flow-generating device in order to beable to lower the grinding device as far as possible in the container.

In terms of abstraction of the idea of the invention, the couplingrepresents a force-transmitting element between the shaft and thehousing. That coupling can be of any desired configuration.

The coupling is preferably in the form of a shaft coupling which ispositively lockingly yielding but rotationally stiff, that is to say acompensating coupling. In the lowered position of the grinding devicethe two coupling elements fit into each other and transmit the torque.At the same time, lengthwise extension of the shafts, which occurs dueto the effect of heat in operation of the arrangement, is compensated.By way of example the coupling can be in the form of a dog coupling,wherein a first dog which forms the first coupling element of thecoupling is arranged at the lower end of the housing and a correspondingsecond dog which represents the second coupling element is arranged atthe lower end of the shaft. An arcuate tooth coupling has proven to beparticularly advantageous, which has a crowned external tootharrangement on the second coupling element which is in the form of apinion and which can move pivotably and axially in the internal tootharrangement of the second coupling element.

In a more complex configuration, the coupling can also be in the form ofa barrel coupling. Although the use of a friction coupling is basicallyalso a possibility, the above-mentioned arcuate tooth coupling enjoysthe advantage that it is very stable and inexpensive; in addition it isparticularly easy to clean and is therefore advantageous in terms ofmaintenance procedures.

For mounting the shaft in the grinding device in the lowered position,it has proven to be particularly advantageous for the drive elementwhich represents a force-transmitting element to be in the form of abearing block. That bearing block accommodates either plain or rollingbearings for supporting the shaft; a double-rolling bearing isparticularly maintenance-friendly and has a long bearing service life.By virtue of the provision of only a small frictional gap between thebearing block and the agitator tool, with a preferable gap size of athird of the bead diameter, in particular between 0.03 mm and 5 mm,particularly preferably 2 mm, the grinding medium is effectivelyprevented from passing therethrough. With the dispersing apparatusaccording to the invention therefore no ‘bead breakage’ occurs.

The dispersion material, that is to say the product flow, can be usedfor cooling and preventing the bearings from running dry, in order toachieve a long bearing service life. For that purpose the dispersionmaterial passes in through the above-mentioned gap at the upper end ofthe bearing block and flows through the bearings to the lower endthereof. The resulting product flow of the medium effectively preventspartial heating of the product and damage to the dispersing apparatus.At the same time however the product flow is sufficiently great topermit simple and quick cleaning upon a change in product.

To increase the flow speed and thus also the cooling capacity, aconveyor screw can be arranged between the rolling bearings in the caseof a doubled rolling bearing.

In addition, for further enhancing the flow speed, it is advantageousif, above the second coupling element, the bearing block has at leastone suction bore through which the product flow is drawn by means of theflow-generating device.

It is particularly advantageous in terms of maintenance procedure forthe bearing block to be integrated into the base of the housing of thegrinding device. For example the bearing block can be easily replacedand cleaned by replacing the circular disc at the lower end of thegrinding basket.

The shaft can have an upper and a lower portion, wherein the lowerportion is of a slightly wider outside diameter than the upper portion.That ensures, in the raised position of the grinding device, that thereis a sufficient gap between the bearing block and the shaft, to avoiddamage to the bearing block. In the lowered position in contrast thebearing block rests on the lower portion of the shaft of the wideroutside diameter and thus ensures satisfactory sealing integrity betweenthe bearing block and the shaft.

As already mentioned above the bearing block, in the lowered position,transmits the shaft torque to the agitator tool within the housing ofthe grinding device. The agitator tool can be of a design configurationwhich depends on the dispersing task involved. It can be for example inthe form of a circular ring disc, a circular ring apertured disc, or aslit disc. The use of pins is also possible. Preferably the agitatortool has at least one circular ring disc which extends in coaxialrelationship within the housing. The agitator tool thus ensures acontinuous movement of the grinding medium disposed in the housing.

In an advantageous configuration of the invention the flow-generatingdevice has dispersing means. It is particularly advantageous if thosedispersing means are in the form of a dissolver disc. Then, on the onehand the dissolver disc generates the flow necessary for operation ofthe dispersing apparatus and in addition effects pre-dispersing of thegrinding medium. The dissolver disc performs a particularly importantfunction in regard to the dispersing effect, namely uniform circulationof product into the edge zone of the mixing container. A dissolver discperforms the functions of the dispersing operation, that is to saybreaking up agglomerates and wetting the primary particles in the liquidphase, in a particularly economic manner, as the dispersing operation iscompleted markedly more quickly than within the grinding device.

Accordingly the dispersing apparatus according to the invention isdesigned in such a way that the grinding device is adjustable in respectof height and by means of the heightwise adjustment it can be dippedinto the dispersion material and can be completely removed therefromagain.

In that way, the individual method steps involved in pre-dispersing andfine dispersing can be effected completely separately from each other,without in that case the substances which are to be dispersed having tobe removed from the container or without the need for a change in theagitator tools. A change between pre-dispersing and fine dispersing canbe effected particularly quickly and economically.

The invention is illustrated by way of example in the drawing anddescribed hereinafter in detail with reference thereto. In the drawing:

FIG. 1 shows a view in cross-section through the dispersing deviceaccording to the invention with the grinding device in the raisedpre-dispersing position,

FIG. 2 shows the dispersing apparatus of FIG. 1 with the grinding devicein the lowered fine dispersing position, and

FIG. 3 shows a view on an enlarged scale in cross-section of thegrinding device of FIG. 1.

Accordingly the dispersing apparatus according to the inventioncomprises a substantially cylindrical, double-wall container 10 which isclosable with a cover, a dissolver 20 and an agitator ball mill 30. Acleaning device which is not shown in detail here can also be arrangedin the container.

The dissolver 20 comprises a cylindrical shaft 21 which has a dissolverdisc 22 at its lower end. The dissolver disc 22 is provided along itsperiphery with a plurality of teeth 23 which are bent alternatelyupwardly and downwardly on the circular surface. The shaft 21 has acentral portion 24, of a first outside diameter, which at its lower endgoes into a lower portion 25 whose outside diameter is greater than thatof the central portion.

The shaft 21 is fixed by way of a cylindrical bearing flange 26 to anupper machine portion 60 which encloses the bearing flange in a box-likefashion. To guarantee the necessary stability, the bearing flange 26preferably extends over more than a third of the total shaft length. Inthe present embodiment, the agitator ball mill 30 is adjustable inrespect of height by way of pneumatic cylinders 62, the piston rods 64of which are mounted to an intermediate plate 66. A plurality of hollowbars 33 extend from the underside of the intermediate plate 66 to theupper end of the agitator ball mill 30. By virtue of that configuration,the arrangement of the agitator ball mill 30 can be displaced verticallyby means of the pneumatic cylinders 62; in addition, the coolant cancirculate in the agitator ball mill 30 by way of the hollow bars.Instead of the pneumatic cylinders, it is possible to use otheradjustment means such as for example hydraulic cylinders or a wormdrive.

The shaft 21 is supported in the bearing flange 26 by way of rollingbearings, wherein a needle bearing or roller bearing 27 is provided atthe lower end of the bearing flange 26 and a double self-aligningbearing 28 at the upper end. The shaft 21 is driven in known manner byway of a belt pulley 29. To reinforce the bearing flange 26, a pluralityof stiffening ribs 32 are provided at the upper end in peripherallymutually displaced relationship. The ribs 32 extend from approximatelythe centre of the bearing flange 26 to the horizontal flange which isthe upper flange in the installation position, at a continuous slope.Those stiffening ribs 32 impart a markedly higher level of stability tothe bearing flange 26 in comparison with the bearing flanges known fromthe state of the art in order to prevent unwanted deflection of theshaft 21, in particular in the pre-dispersing operation.

The agitator ball mill 30 is fixed by way of a plurality of cylindricalhollow bars 33 which are peripherally spaced relative to each other tothe underside of the upper machine portion 60 by way of the intermediateplate 66 so that the agitator ball mill 30 is adjustable in respect ofheight, with the upper machine portion 60, by means of the pneumaticcylinders 62. Instead of the pneumatic cylinders it is also possible touse other adjustment means such as for example hydraulic cylinders or aworm drive.

The agitator ball mill 30 itself comprises a housing 34 which isperforated sieve-like and in which grinding balls (not shown) are held.At its upper end, the housing 34 is provided with a funnel which at itsbase has an opening 35 through which the shaft 21 passes. The housing 34can be of a single-wall structure, a double-wall structure or can be ofanother suitable structure. The housing 34 forms an annular passage withthe central hole 35. A circular ring disc 36 is disposed within theannular passage extending in coaxial relationship therewith.

At its upper end the circular ring disc 36 is connected by way of a ringdisc 37 to a bearing block which is identified generally by reference39. That bearing block comprises a cylindrical bush 40 which is centeredon the lower shaft portion 25 in the lowered position and which at itslower end has an outwardly enlarging step 41. A double rolling bearing42 is supported on the step 41, the bearings being spaced from eachother by an outside spacer ring 43. Arranged radially inwardly from thespacer ring 43 between the bearings of the double rolling bearing 42 isa conveyor screw 44. The double rolling bearing 42 is supported at thetop side relative to the underside of the ring disc 37 by way of afurther spacer ring 45. A bladed impeller 46 is arranged on a radiallyexternal step of the ring disc 37 in order to provide an increased flowof product out of the container into the housing 34 and at the same timeto prevent unwanted escape of the grinding balls out of the agitatorball mill in operation of the assembly. Provided at the lower end of thebearing block 39 beneath the step 41 of the bush 40 is the internaltooth arrangement 47 of an arcuate tooth coupling representing the firstcoupling element for transmission of torque from the shaft 21 to thering disc 36. A plurality of suction bores 48 are arranged inperipherally mutually spaced relationship between the internal tootharrangement 47 and the step 41 of the bush 40. Radially outwardly thebearings of the double rolling bearing arrangement 42 are supportedagainst the inside of a hollow truncated cone 49 which taperscontinuously from its lower cylindrical portion to its upper end andwhich is supported with an internal step on the upper bearing of thedouble rolling bearing 42.

Between the inside of the upper end of the hollow truncated cone 49,above the upper bearing, there is a gap of approximately 0.3 mm betweenthe hollow truncated cone 49 and the second spacer ring 45. The productflow can pass through that gap during operation for cooling the bearingsand preventing them from running dry. That configuration prevents theingress of beads or grinding balls and thus also prevents the feared‘bead breakage’. The product flow flows continuously through thebearings to provide a self-cooling effect, due to the conveyor screw 44and the suction bores 48.

The hollow truncated cone is screwed by way of a plurality ofperipherally arranged screws 50 to an inner ring element of a circulardisc portion 51. That disc portion 51 forms the base of the agitatorball mill 30 and accommodates a sieve 52 which extends from an innerring element of the disc portion 51 radially outwardly to an outer ringelement. The medium flows through that sieve 52 during the finedispersing operation and separates the ground material from the beads.

Provided above the dissolver disc 22 and below the lower shaft portion25 is an external tooth arrangement 53 forming the second couplingelement. Upon downward movement of the agitator ball mill 30 out of thepre-dispersing position shown in FIG. 1 into the fine dispersingposition shown in FIG. 2 the bush 40 is displaced on to the lower shaftportion 25 until the internal tooth arrangement 47 comes into engagementwith the external tooth arrangement 53. The arcuate tooth coupling nowtransmits the shaft torque to the circular ring disc 36 for performingthe fine dispersing operation.

The configuration of the upper shaft portion 24 which is of a smalleroutside diameter than the lower shaft portion 25 ensures that there is asufficient gap between the shaft 21 and the agitator ball mill 30 in thepre-dispersing position to prevent undesirable damage to the bush 40 dueto possible lateral deflection movements of the shaft 21 during thepre-dispersing operation.

The arrangement according to the invention of the coupling at the lowerend of the agitator ball mill makes it possible to dispense with thehollow shaft found in the state of the art, but at the same time furtherto combine a pre-dispersing device and a fine dispersing device in oneunit, wherein the change between the method steps can be effected simplyby lowering the agitator ball mill within the container without thecontainer having to be opened. Instead of a positively locking coupling,it will be appreciated that it is also possible to use a couplinginvolving a force-locking relationship to carry the idea of theinvention into effect, such as for example a plate coupling or the like.Finally, instead of rolling bearings in the bearing block, it is alsopossible to use plain bearings.

LIST OF REFERENCES

-   10 container-   20 dissolver-   21 shaft-   22 dissolver disc-   23 teeth-   24 central shaft portion-   25 lower shaft portion-   26 bearing flange-   27 needle bearing-   27 roller bearing-   28 double self-aligning bearing-   29 pulley-   30 agitator ball mill-   32 stiffening ribs-   33 hollow bar-   34 housing-   35 opening-   36 circular ring disc-   37 ring disc-   39 bearing block-   40 bush-   41 step-   42 double rolling bearing-   43 spacer ring-   44 conveyor screw-   45 spacer ring-   46 impeller-   47 internal tooth arrangement-   48 suction bore-   49 hollow truncated cone-   50 screw-   51 circular disc portion-   52 sieve-   53 external tooth arrangement-   60 upper machine portion-   62 pneumatic cylinder-   64 piston rods-   66 intermediate plate

1. A dispersing apparatus for arrangement in a container for adispersion material, comprising a flow-generating device drivable by ashaft and a grinding device which contains a grinding medium and whichhas a perforated housing through which the dispersion material can passby virtue of a flow generated by the flow-generating device, and anagitator tool which is drivable by a drive element and which is arrangedin the housing and is rotatable relative thereto, wherein the housingencloses the shaft, wherein the housing is displaceable relative to theshaft from a raised position into a lowered position, and wherein theshaft and the drive element can be coupled together by way of a couplingwhich has a first element and a corresponding second element, whichelements come into operative relationship in the lowered position,characterized in that the first coupling element is arranged at a lowerend of the housing and that the second coupling element is arranged inthe region of a lower end of the shaft.
 2. A dispersing apparatusaccording to claim 1 characterized in that the second coupling elementis arranged at the lower end of the shaft.
 3. A dispersing apparatusaccording to claim 1 characterized in that the coupling is in the formof a longitudinally movable compensating coupling.
 4. A dispersingapparatus according to claim 1 characterized in that the drive elementincludes a bearing block.
 5. A dispersing apparatus according to claim 4characterized in that the bearing block has a double rolling bearing. 6.A dispersing apparatus according to claim 5 characterized in that aconveyor screw is disposed between the rolling bearings.
 7. A dispersingapparatus according to claim 4 characterized in that the bearing blockhas at least one suction bore above the second coupling element.
 8. Adispersing apparatus according to claim 4 characterized in that thebearing block is integrated into the base of the housing.
 9. Adispersing apparatus according to claim 1 characterized in that theshaft has a central portion and a lower portion and that the lowerportion is of a larger outside diameter than the central portion.
 10. Adispersing apparatus according to claim 1 characterized in that theflow-generating device is in the form of a dissolver disc.